This invention relates to an oxidation process, and apparatus therefor, and in particular to the reaction of nitrous oxide with metals and metal oxides.
When nitrous oxide is contacted with certain metals, e.g. copper, iron, cobalt, nickel, and silver, or with certain metal oxides that can be oxidised to a higher state, e.g. magnetite, the nitrous oxide is decomposed, oxidising the metal or metal oxide (hereinafter termed the active material) and producing nitrogen (see, for example, Trans. Faraday Soc 65, 1969, pages 2465-73). This reaction occurs only at the surface of the active material and so can be used to determine the surface area of the active material, particularly where the active material has a high surface area, typically above about 1 m.sup.2.g.sup.-1, as is often the case in materials for use as catalysts.
Heretofore three methods making use of this reaction have been employed for determination of surface areas, viz gravimetric, static, and pulsed flow, techniques.
The gravimetric method simply involves determining the weight of the sample before and after exposure to nitrous oxide. Provided care is taken good accuracy can be achieved. However the technique is time consuming and not suited to routine measurements, e.g. as part of a quality control procedure in catalyst manufacture.
The static method involves leaving the sample in contact with nitrous oxide in a sealed apparatus, then cooling to liquefy the excess of nitrous oxide and measuring the amount of nitrogen produced. This technique again is inconvenient, time consuming, and gives only a moderate accuracy.
The pulsed flow method involves contacting the sample periodically with pulses of a known amount of nitrous oxide and determining the nitrogen/nitrous oxide ratio in the exit gas corresponding to each pulse. Again the technique is inconvenient, time consuming and gives only a poor accuracy: we have found that this technique often gives an accuracy of no better than .+-.10%.